Use of biotin or a biotin derivative for lightening skin and treating age spots

ABSTRACT

The present invention relates to the use of biotin alone, preferably, however, with vitamin C or a derivative thereof, for the preparation of a cosmetic composition or of a pharmaceutical composition for skin-lightening purposes, for the elimination of skin color irregularities and for the treatment of senile lentigines.

The present invention relates to the use of biotin or a biotinderivative alone, preferably with vitamin C or a vitamin C derivative,for the preparation of a pharmaceutical composition or a cosmeticcomposition for the treatment of senile lentigines, for smoothening skincolor irregularities and/or for lightening natural skin color.

Senile lentigines are dark spots on the skin arising from the aging ofthe skin. They are a consequence of various aging processes, which areaccelerated by incident light radiation. The skin thus appearsinhomogeneous with respect to its color.

Tanning is a natural protective function of the skin with varyingdegrees of distinction in different ethnic groups. In many culturalcircles a light skin tone is considered attractive so that a need forlightening the natural skin color arises.

Compositions for skin lightening purposes are known, such as e.g.hydroquinone, kojic acid, arbutin, vitamin C as well as various plantextracts. One problem with many compositions, however, is that apartfrom a lightening of the skin or an elimination of the senile lentigos(liver spots, senile lentigines) also side effects such as e.g. skinirritations can occur. Plant extracts that lead to fewer skinirritations are generally not sufficiently effective.

There is a need for additional compositions, particularly cosmeticcompositions that are well tolerated by the skin and yet are effectivefor skin lightening, for the treatment of senile lentigines and forsmoothening skin color irregularities. The compositions should be atleast as effective, preferably more effective than the familiar skinlightening compositions.

Biotin is a known active ingredient, which can be found in numerouscosmetic formulations and pharmaceutical compositions. Biotin is acompound of the following formula:

that can occur in eight different stereoisomeric forms. Biotin is inparticular the D-(+)-biotin, i.e. the compound(3aS,4S,6aR)-2-oxohexahydrothieno[3,4-d]-imidazole-4-valeric acid of thefollowing formula:

The effectiveness of the use of biotin in skin lightening applicationshas not been known until now.

Pursuant to the invention it was surprisingly found that biotin exhibitsa skin-lightening effect and thus can be used for the treatment ofsenile lentigos, for smoothening skin color irregularities as well asfor lightening the natural skin tone.

The invention hence makes the use of biotin available for thepreparation of a composition for lightening the natural skin tone, forsmoothening skin color irregularities and/or for treating senilelentigines.

The term “biotin” pursuant to the invention relates to the eightstereoisomers of the formula:

either in a stereochemically pure form or as any random mixture of twoor more stereoisomers. Particularly preferred pursuant to the inventionis the D-(+)-biotin of the formula:

Biotin derivatives are known to the expert. These are compounds that areconverted into biotin in vitro, particularly however in vivo. Lipophilicbiotin derivatives, which generally penetrate the skin better thanbiotin itself, yet achieve equivalent effects as biotin, areparticularly preferred. Apart from biotin, pursuant to the inventionalso biotin esters are particularly preferred, from which afterpenetration through the stratum corneum biotin is released again by theskin's own enzyme systems. Particularly preferred pursuant to theinvention are biotin esters of the formulas I and II, which are deducedfrom biotin as follows:

wherein

R₁═H, C₁-C₂₀-alkyl, C₅-C₇-cycloalkyl, aryl;

R₂ and R₃=independent from each other H, C₁-C₅-alkoxycarbonyl; and

R₄═H, C₁-C₂₀-alkyl, C₁-C₅-alkoxycarbonyl.

A C₁-C₂₀-alkyl radical is preferably a C₁-C₁₀-alkyl radical, even morepreferred a C₁-C₆-alkyl radical such as a methyl, ethyl, n-propyl,iso-propyl, n-butyl, tert.-butyl or an iso-butyl group.

A C₅-C₇-cycloalkyl radical is preferably a cyclohexyl group.

An aryl radical is preferably a C₅-C₁₀-aryl radical, in particular aphenyl group.

A C₁-C₅-alkoxycarbonyl radical is preferably a C₁-C₃-alkoxycarbonylradical.

The radical R₁ is preferably a hydrogen atom or a C₁-C₆-alkyl radical.

At least one of the radicals R₂ or R₃ is preferably a hydrogen atom,even more preferred both radicals R₂ and R₃ are hydrogen atoms. Theradical R4 is preferably a hydrogen atom or a C₁-C₆-alkyl radical, evenmore preferred a hydrogen atom.

The radicals R₂, R₃ and R₄ are particularly preferred all hydrogenatoms, and the radical R₁ is a C₁-C₆-alkyl radical, as defined above.

Among the biotin derivatives, all stereoisomeric forms and salts areincluded pursuant to the invention either alone or in random mixtures.

Pursuant to the invention, biotin and the derivatives thereof can beused individually, however it is also possible to employ a mixture ofbiotin and one or more of its derivatives, for example biotin in amixture with one or more biotin esters, as defined above. Likewisevarious biotin derivatives can be employed in mixtures with each other.

The preparation of biotin derivatives is known to the expert, and inthis respect conventional standard methods of organic chemistry can beused, e.g. the esterification of biotin with the desired alcohol such asmethanol or ethanol by splitting off water.

The biotin and the biotin derivatives can likewise be used in the saltform. Suitable biotin salts are not particularly limited, and in thiscontext salts with alkalis, alkaline earths and other suitable metals,but also with ammonium and organic bases, especially sodium, potassium,calcium and magnesium salts, can be mentioned. Due to the nitrogenatoms, the biotin and especially also the biotin derivatives can existalso in the form of an acid addition salt upon reaction with a suitableacid, such as an inorganic or organic acid, especially a mineral acid,e.g. with HCl. The hydrochloride salt is particularly preferred.Preparation of the salts occurs in the familiar fashion e.g. throughreaction of the biotin or a derivative thereof with the correspondingbase (e.g. NaOH or KOH) or the corresponding acid (e.g. HCl).

To the extent that within this description a “composition” is mentionedwithout more detailed specification, it should be understood both as acosmetic composition and a pharmaceutical composition. To differentiatebetween cosmetic compositions and pharmaceutical compositions pleaserefer e.g. to Rompp, Chemical Encyclopedia, 10th Edition and theliterature cited therein. Pursuant to the invention biotin is preferablyused for the production of a cosmetic composition in which the biotin isformulated together with additives that are compatible with cosmetics.Pursuant to the invention it is, however, also possible to use biotinfor the production of a pharmaceutical composition, wherein the biotinis formulated with additives that are compatible with drugs. To theextent that within the framework of this application no otherexplanations are provided, the additives that are mentioned areadditives that are compatible with cosmetics as well as additives thatare compatible with drugs.

Pursuant to the invention, the compositions into which biotin isformulated are preferably topical compositions, such as e.g. liquid orsolid oil-in-water emulsions, water-in-oil emulsions, multipleemulsions, micro-emulsions, PIT emulsions, Bickering emulsions,hydrogels, alcoholic gels, lipo-gels, single- or multiple-phasesolutions, foams, ointments, plasters, suspensions, powders, creams,cleansers, soaps and other conventional compositions, which can also beapplied e.g. by means of sticks, masks or as sprays.

The topical compositions preferably contain one or more additives, suchas, for example, carriers and/or supplementary or auxiliary agents thatare compatible with cosmetic and/or pharmaceutical compositions, as theyare generally used in such preparations. Here for example fats, oils,waxes, silicones, emulsifiers, alcohols, polyhydric alcohols, thickeningagents, moistening and/or moisture-retaining substances, surfactants,softening agents, foam-retarding agents, anionic, cationic, non-ionic oramphoteric polymers, alkanization or acidification agents, watersofteners, adsorbents, sun-screen agents, electrolytes, sequesteringagents, water, organic solvents, preservatives, bactericides,anti-oxidants, vitamins, scents, aromas, sweetening agents, colorantsand pigments can be mentioned.

The topical formulations pursuant to the invention preferably containone or more conventional fatty substances as additives, e.g., vegetableoils, liquid paraffin oils, isoparaffin oils, synthetic hydrocarbons,di-n-alkyl esters, fatty acids, fatty alcohols, ester oils,hydroxy-carboxylic acid esters, di-carboxylic acid esters, diol esters,symmetrical, non-symmetrical or cyclic esters or carbonic acid esterswith fatty alcohols, mono-, di- and tri-fatty acid esters with glycerin,waxes and silicon compounds.

The fatty substances are generally present in the topical composition ina quantity of 0.1 to 50% by weight, preferably from 0.1 to 20% byweight, in particular from 0.1 to 15% by weight (in relation to theentire composition, respectively).

The topical compositions can contain other additives, such as, forexample, one or more surface-active substances as emulsifying ordispersing agents. Suitable examples of such emulsifying or dispersingagents are known.

The emulsifying agents can be present in the topical compositions forexample in parts from 0.1 to 25% by weight, preferred from 0.5 to 15% byweight, in relation to the entire composition.

The topical compositions can likewise contain conventional sun-screenagents as additives, for example conventional UV-A and/or UV-B filters.An overview of conventional UV-A and UV-B filters, which can also beemployed in the compositions pursuant to the invention, can be found forexample in EP-A 1 081 140. Pursuant to the invention of course alsonovel sun protection filters that are disclosed in this document for thefirst time can be used in the inventive compositions.

Suitable organic, mineral or modified mineral sun-screen filters arealso disclosed in WO 01/64177, to which we refer here as well.

If desired, the inventive compositions can also contain proteinhydrolyzates or derivatives thereof as well as suitable mono-, oligo- orpoly-saccharides or their derivatives, as additives, as they are e.g.revealed in WO 01/64177. Further suitable additives and auxiliaryagents, such as vitamins, pro-vitamins and vitamin precursors,allantoin, bisabolol, anti-oxidants, ceramides and pseudo-ceramides,triterpenes, monomer catechines, thickening agents, plant glycosides,structure-providing substances (structuring agents), dimethylisosorbide,solvents, swelling and penetration adjuvants, perfume oils, pigments andcolorants for dying the composition, substances for adjusting the pHvalue, complexing agents, opacifiers, pearly luster substances,expanding agents, film-forming, emulsion-stabilizing, thickening oradhesive polymers, especially cationic, anionic as well as non-ionicpolymers are likewise revealed in WO 01/64177, which is incorporatedherein by reference in so far.

The compositions are preferably formulated such that they are suitablefor topical applications. Topical application occurs preferably at leastonce a day, e.g. two or three times a day. The treatment durationgenerally lasts at least two days until the desired effect has beenachieved. The treatment duration can also take several weeks or months.

The quantity of the composition that is to be applied depends on theconcentration of the active ingredient in the composition as well as theseverity of the disease that is to be treated and/or the desiredcosmetic success. In the case of a pharmaceutical usage generally thequantity of the active ingredient to be used per application is higherthan in the case of a cosmetic use. An effective amount for theapplication depends on the condition of the skin, the person to betreated as well as the severity and type of the skin discoloration to betreated and other factors, which are known to the attending physician orcosmetician. For example application can occur such that a cream isapplied to the skin. A cream is usually applied in a suitable quantityof 2 mg cream/cm² skin. The applied quantity however is not critical,and if no treatment success should be achieved with a certain quantityof the applied active ingredient then the applied amount can certainlybe increased, for example by using topical formulations with higherconcentrations.

Pursuant to the invention the active ingredient can be formulated assuch or also in encapsulated form, for example in liposomal form.Liposomes are beneficially formed with lecithins without or with theaddition of sterols or phytosterols. The encapsulation of the activeingredient can occur alone or together with other active ingredients.

The inventive composition contains a suitable quantity of 0.0001% byweight to approximately 50% by weight of biotin in relation to the totalweight of composition. It is more preferred if biotin is present in asuitable quantity of 0.01% by weight to about 20% by weight, even morepreferred in a suitable quantity of about 0.01% by weight to about 1% byweight, in particular in a suitable quantity of about 0.1% by weight inrelation to the total weight of the composition.

With respect to the type and preparation of the topical compositions aswell as the disclosure of exemplary additives, we would like to refer torelevant literature, e.g. to NOWAK G. A., Cosmetic Preparations—Volume2, Cosmetic Preparations—Recipes, Starting Substances, Scientific Basis(Verlag fur chem. Industrie H. Ziolkowsky K G, Augsburg, Germany).

It is likewise possible to formulate biotin as an oral composition, forexample in form of pills, tablets, capsules, which e.g. contain agranule or pellet, as liquid oral formulations or as an additive tofoods, which is known to the expert in principle. Suitable methods andadditives, with which the orally administered compositions can beproduced pursuant to the invention, are disclosed e.g. in the standardwork “Remington: The Science and Practice of Pharmacy”, Lippincott,Williams and Wilking (Publisher) 2000, which is incorporated herein byreference.

Traditional excipients such as micro-crystalline cellulose, sodiumcitrate, calcium carbonate, disodium or dipotassium phosphate, sodium orpotassium phosphate, glycine, agents to promote breakdown such as starchor alginic acid, binding agents such as polyvinyl-pyrrolidone,saccharose, gelatin or acacia gum, slip additives such as magnesiumstearate, sodium lauryl sulfate or talcum can be used in tabletproduction as conventional additives for oral compositions, especiallyfor tablets. If the composition is filled in gel capsules, conventionalauxiliary agents for the production of granules are lactose or milksugar as well as polyethylene glycols with a high molecular weight.Further additives for other oral formulations, and in particular for theformulation as additives to foodstuffs, are known to the expert, and werefer to the relevant literature, e.g. “Principles of Food Engineering”(Grundzoge der Lebensmitteltechnik), Horst-Dieter Tscheuschner(publisher), 2nd, newly revised Edition Hamburg: Behr's 1996.

In case of an oral composition, the content of the active ingredient(i.e. the biotin and/or biotin derivative) in the composition isgenerally 1% to 90%, preferably 10% to 80%, e.g. 50% or more.Administration occurs such that the desired effect is achieved anddepends on the condition of the patient, the type and severity of theskin discoloration to be treated, etc. and can easily be determined bythe expert. A common daily dosage of the active ingredient is in therange from 0.1 μg/day to 50 mg/day, e.g. 20 μg/day to 2 mg/day.

Pursuant to the invention it was furthermore surprisingly found thatapart from its own effectiveness for skin lightening purposes biotinexhibits a surprisingly high skin-lightening effect when it isadministered together with vitamin C or a vitamin C derivative.

Vitamin C derivatives are known, and pursuant to the invention they areinterpreted as all compounds that release vitamin C in vivo or in vitro,as well as solvates, hydrates and salts thereof. As examples of vitaminC derivatives e.g. glucosides of ascorbic acid and phosphates ofascorbic acid and in particular magnesium ascorbyl phosphate, sodiumascorbyl phosphate, calcium ascorbyl phosphate, potassium ascorbylphosphate and mixed salts, such as e.g. sodium magnesium ascorbylphosphate or sodium calcium ascorbyl phosphate, can be mentioned.Especially the phosphates frequently exist as hydrates, wherein thedihydrate form is the most common. Biotin is particularly preferredpursuant to the invention together with sodium ascorbyl phosphate, andthe most preferred in form of the dihydrate, as it is available forexample from Roche Vitamins AG under the product name STAY-C 50.

It has been known that vitamin C exhibits a skin-lightening effect, yetit was not known that a combination of biotin and vitamin C and/or avitamin C derivatives have a skin-lightening effect that is considerablymore distinct than the skin-lightening effect of vitamin C alone.

Pursuant to the invention the vitamin C and/or the derivatives thereofcan be incorporated in the same formulation in which also the biotin ispresent. Vitamin C and/or the derivative thereof in a topicalcomposition is preferably used in a quantity of 0.001% by weight toabout 50% by weight in relation to the total weight of the composition.It is more preferred if vitamin C and/or the derivative thereof is usedin a topical composition in a quantity of 0.01% by weight to about 20%by weight, even more preferred in a quantity of about 0.1% by weight toabout 15% by weight, e.g. 1 to about 5% by weight, such as e.g. 3% byweight, in relation to the overall weight of the composition. Withrespect to the quantity of vitamin C and/or the derivative thereof in anoral composition we would like to refer to the aforementionedexplanations of biotin which also applies to the quantity and dosage ofvitamin C and/or the derivative thereof.

Pursuant to the invention, the term “composition” also includes anembodiment in which the composition is present in two separate parts,wherein one part contains the active ingredient biotin and the otherpart the active ingredient vitamin C or a derivative thereof. The twoseparate parts of the composition can each be topically applied ororally ingested, yet it is also possible that one separate part of thecomposition is applied topically and the other part of the compositionis administered orally so that in the inventive composition e.g. oneseparate part contains the active ingredient biotin and is appliedtopically, while the other separate part contains the active ingredientvitamin C or a derivative thereof and is administered orally or whereinthe separate part of the composition that contains the active ingredientbiotin is administered orally and the separate part of the compositionthat contains the active ingredient vitamin C and/or a derivativethereof is applied topically.

For the preparation of the separate parts of the composition, theadditives, active ingredients and the quantities of the respectiveadditives and active ingredients contained in the separate parts,reference can be made to the aforementioned examples of topical and oralformulations with biotin, which also apply to the inventive embodimentin which the composition exists in two separate parts, each containingan active substance. For the quantity of vitamin C and/or the derivativethereof in one of the separate parts, reference can be made to theaforementioned embodiments wherein the composition is not present in theform of two separate parts, but where both active ingredients arepresent in a single composition.

To the extent that the composition contains both biotin and vitamin Cand/or a derivative thereof, the weight ratio of vitamin C and/or thederivative thereof to biotin is preferably 500:1 to 1:500, morepreferred 100:1 to 1:100, and in particular 30:1 to 1:30. It isfurthermore preferred that the quantity of vitamin C and/or thederivative thereof is higher in the composition than the quantity ofbiotin. The information above applies both to embodiments in whichbiotin and vitamin C and/or a derivative thereof are present together inthe mixture and to embodiments in which the composition consists of twoseparate parts, wherein the one part contains the active ingredientbiotin and the other part the active ingredient vitamin C and/or aderivative thereof.

To the extent that the active ingredients mentioned here can be presentas hydrates or solvates, the hydrates and solvates are also included inthe present invention.

Pursuant to the invention a composition that contains both activeingredients together in a mixture is preferred, particularly preferredis a composition that is administered topically.

The following examples are provided to further illustrate the process ofthe present invention.

1. FORMATION EXAMPLE

A cream was produced in the familiar fashion from the followingcomponents: Ingredients INCI Description % w/w A) Brij 721 Steareth 214.00 Brij 72 Steareth 2 2.00 Lanette O Cetearyl Alcohol 2.00 GlycerylMyristate Glyceryl Myristate 3.00 Oleic Acid Oleic Acid 6.00 Tegosoft MIsopropyl Myristate 3.00 Estol 1517 Isopropyl Palmitate 3.00 TranscutolCG Ethoxydiglycol 5.00 Phenonip Phenoxyethanol & Methylparaben & 0.80Ethylparaben & Propylparaben & Butylparaben Dow Corning 200, Dimethicone0.50 350 cs BHT Butylated Hydroxytoluene 0.05 B) Deionized water Aqua Ad100   Propylene Glycol Propylene Glycol 5.00 Edeta BD Disodium EDTA 0.10Keltrol T Xanthan Gum 0.20 Carbopol ETD 2001 Carbomer 0.30 C) TEA 99%Triethanolamine qs pH 7 Biotin Biotin 0.10 Deionized water Aqua 10.00 D) Deionized water Aqua 6.00 STAY-C 50 Sodium Ascorbyl Phosphate 3.00

Parts A) and B) were heated separately from each other to 75° C.,respectively, while stirring. As soon as parts A) and B) werehomogeneous, part B) was added to part A) while stirring. The mixturewas homogenized at 11,000 RPM for 30 seconds. Part C) was pre-warmed to65° C. and added to the homogenized mixture of A) and B). The mixture ofA), B) and C) was cooled down to 40° C., and part D) was added. Themixture was cooled down to the ambient temperature (25° C.) whilestirring.

The resulting cream had a pH value of 7.0 and had a viscosity(Brookfield RVT, 25° C., Spindle 5, 10 RPM) of approximately 20,000 cP.

Apart from a cream pursuant to the invention, a placebo was producedcorrespondingly, in which neither sodium ascorbyl phosphate nor biotinwere present, as well as a cream with 0.1% biotin exclusively and acream with 3% sodium ascorbyl phosphate exclusively.

2. TEST EXAMPLE

39 female subjects were divided into three groups of 13 persons each.The subjects applied twice a day for three months a test formulation onthe left and a second test formulation on the right halves of theirfaces as well as on the left and the right backs of their hands. Thetest formulations were coded and corresponded to a placebo formulationand a formulation with the desired test substance. The three groupshereby tested the creams produced above with 3% sodium ascorbylphosphate (STAY-C 50), 0.1% biotin and with a mixture of 3% sodiumascorbyl phosphate and 0.1% biotin.

A CR 300 chromometer was used to measure the lightening of the senilelentigines. The values that were obtained were provided as ITA° values.ITA° describes the pigmentation degree of the skin and/or the senilelentigines. The values reflected below correspond to the differences inITA° values over the base line before start of the study. The higher thevalue, the greater the lightening of the skin. The ITA° values weredetermined after 29, 57 and 85 days, i.e. after approximately one month,after about two months and after about three months. The results areshown in the following table. ITA° ITA°-p-values Composition Day 29 Day57 Day 85 Day 29 Day 57 Day 85 Placebo 1.53 7.67 9.29 0.381 0.953 0.8573% NAP 4.46 7.53 8.80 Placebo 2.75 5.93 8.07 0.156 0.480 0.217 0.1%Biotin 5.57 7.55 11.16 Placebo 3.32 6.89 9.70 0.055 0.006 0.045 3% NAP +7.16 11.65 13.42 0.1% Biotin

The study was conducted during the winter months, and during this timethe skin lightens naturally. This explains why also the placeboformulations led to a slight skin lightening. The skin lightening effectfor the placebo formulations however is only small.

Surprisingly biotin had a skin lightening effect already at aconcentration of 0.1%, which is greater after one and three months andabout as high as that of the known skin lightening composition vitamin Cafter two months. The very high skin lightening effect of a mixture of3% sodium ascorbyl phosphate and 0.1% biotin was particularlysurprising.

The results of the study are shown in FIGS. 1 through 3.

1. A method of making composition for lightening the skin and/orsmoothening skin color irregularities comprising admixing biotin, abiotin derivative or a salt thereof with a cosmetic additive orpharmaceutical additive.
 2. A method of making a composition forlightening the skin, smoothening skin color irregularities and/ortreating senile lentigos comprising admixing biotin, a biotin derivativeor a the salt thereof with vitamin C or a vitamin C derivative.
 3. Amethod according to claim 1, wherein the biotin salt is an alkali salt,an earth alkali salt, an ammonium salt or a hydrochloride of the biotinor the biotin derivative.
 4. A method according to claim 1, wherein thebiotin derivative is a compound of formula I or formula II:

wherein R₁ is H, C₁-C₂₀-alkyl, C₅-C₇-cycloalkyl, or aryl; R₂ and R₃ areeach independently H or C₁-C₅-alkoxycarbonyl; and R₄ is H, C₁-C₂₀-alkylor C₁-C₅-alkoxycarbonyl.
 5. A method according to claim 1, wherein thecomposition is for topical administration.
 6. A method according toclaim 1, wherein the composition is for oral administration.
 7. A methodaccording to claim 1, wherein the composition is a cosmetic composition.8. A method according to claim 1, wherein the composition is apharmaceutical composition.
 9. A method according to claim 1, whereinthe biotin, the biotin derivative or the salt thereof is present at aconcentration of 0.001 to 50% by weight, in relation to the weight ofthe composition.
 10. A method according to claim 9 wherein the biotin,the biotin derivative or the salt thereof is present at a concentrationof 0.01 to 1% by weight, in relation to the weight of the composition.11. A method according to claim 2 wherein the biotin, the biotinderivative or the salt thereof is used together with sodium ascorbylphosphate or a hydrate thereof, in particular the dihydrate thereof. 12.A method according to claim 2 wherein the vitamin C or the vitamin Cderivative is present at a concentration of 0.001 to 50% by weight, inrelation to the weight of the composition.
 13. A method Use according toclaim 12, wherein the vitamin C or the vitamin C derivative is presentat a concentration of 0.1 to 15% by weight, in relation to the weight ofthe composition.
 14. A method according to claim 2 wherein the weightratio of the vitamin C or the vitamin C derivative, respectively, to thebiotin, the biotin derivative or the salt thereof is is 500:1 to 1:500.15. A method according to claim 14 wherein the weight ratio of thevitamin C or the vitamin C derivative, respectively, to the biotin, thebiotin derivative or the salt thereof is 30:1 to 1:30.
 16. A methodaccording to wherein the composition is arranged such that the biotin,the biotin derivative or the salt thereof and the vitamin C or thevitamin C derivative, respectively, are physically separated.
 17. Amethod according to claim 16 wherein one of the active ingredients isformulated for oral administration and the other is formulated fortopical administration.
 18. A method according to claim 2, wherein thebiotin salt is an alkali salt, an earth alkali salt, an ammonium salt ora hydrochloride of the biotin or the biotin derivative.
 19. A methodaccording to claim 2, wherein the biotin derivative is a compound offormula I or formula II:

wherein R₁ is H, C₁-C₂₀-alkyl, C₅-C₇-cycloalkyl, or aryl; R₂ and R₃ areeach independently H or C₁-C₅-alkoxycarbonyl; and R₄ is H, C₁-C₂₀-alkylor C₁-C₅-alkoxycarbonyl.